1. Field of the Invention
The present invention relates to a fastener and, particularly, to a fastener capable of speedily screwing.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional countersunk fastener 1 comprises a shank 11, a threaded section 12 spirally arranged on the shank 11, a head 13 connected to one end of the shank 11, and a drilling portion 14 connected to the other end of the shank 11, opposite to the head 13. The head 13 has a top surface 131, a connecting surface 132 connecting the top surface 131 and the shank 11 and shrinking gradually from the top surface 131 to the shank 11, and a plurality of cutting edges 133 equidistantly recessed in the connecting surface 132 by an equal angle. Each cutting edge 133 has two cutting surfaces 134 that are disposed apart and curvedly extended from the top surface to the shank 11. Namely, the cutting edges 133 and the cutting surfaces 134 are concurrently formed into identical curves. In screwing the fastener 1 into an object 2, burrs generated from the threaded section 12 cutting the object 2 travel along the rotating direction of the threaded section 12. Thence, the burrs are guided by the curved cutting edges 133 and the cutting surfaces 134, so that the burrs are pressed into the object 2. Further, the cutting edges 133 and the cutting surfaces 134 are able to flatten the bulge deformed on the object 2 caused by the pressing of the threaded section 12. Moreover, the burrs, bulges, and breakages are preferably avoided. Consequently, after the fastener 1 is driven into the object 2, the surface of the object 2 becomes even.
In practice, the conventional recessions may only be able to accommodate cutting debris in time of screwing. Moreover, the arrangement of the cutting edges 133 is same to the rotating portion of the threaded section 12 while the fastener 1 is driven into the object 2. Therefore, the cutting edges 133 are able to restrain the burrs or the bulges from the object 2. However, the current construction of the fastener still can be improved after practicing. Thus, the present invention is resulted.